Added comments about locking in dns_dbtable struct.
Added comments about locking in dns_dbtable struct.

each/bind9-collab,pecharmin/bind9,each/bind9-collab,pecharmin/bind9,each/bind9-collab,each/bind9-collab,each/bind9-collab,pecharmin/bind9,pecharmin/bind9,pecharmin/bind9,pecharmin/bind9,each/bind9-collab